1. Field of the Invention
The present invention relates to an electronic apparatus driven by for example a battery power source and to a method for controlling a semiconductor integrated circuit, in particular, to a structure and a method for reducing power consumption.
2. Description of the Related Art
Portable electronic apparatuses such as a cellular phone, a personal digital assistant (PDA), and a portable computer normally use a battery as a power source. A battery driven type system comprises a system large scale integrated circuit (system LSI), a battery, and a power controlling integrated circuit (power controlling IC). A system LSI is an LSI chip that has a central processing unit (CPU), a memory, and various peripheral function blocks. Recently, portable electronic apparatuses are also provided with multimedia communication and process functions as well as a communication function. Miniaturized system LSIs having a gate length of for example as narrow as 0.3 μm have been accomplished.
In the battery driven type portable electronic apparatuses such as a cellular phone, their standby time depends on their power consumption. Thus, it is important for these apparatuses to reduce their power consumption. A first related art reference discloses a technology of which the voltage drop of a power source is controlled, while power for a system LSI is always turned on, a clock supplied to an internal circuit such as a CPU is stopped so that power consumption in a standby state is reduced.